Casus belli

Casus belli is a Latin term meaning case of war. In the game, a country with a casus belli (commonly abbreviated to "CB") on another country is deemed to have a valid cause for war. When declaring war, the player is presented with a list of available CBs. They may pick a CB from the list or choose to declare war without a casus belli and accept the penalties of +30 aggressive expansion and −2 stability (halved with full Diplomatic ideas).

Each casus belli has a particular war goal associated with it, generally either controlling a particular province or winning a certain proportion of battles. Meeting the war goal will cause the war score of whichever side has achieved it to gradually rise (up to a max bonus of 25% at a rate of +0.4% per month).

The casus belli also determines what peace terms may be demanded at no or reduced diplomatic power cost; additionally, some CBs disallow some peace terms entirely. Extracting additional concessions beyond those of the original CB (unjustified demands) will cost diplomatic power to be demanded.

List of casus belli

War goals

Each CB has an associated war goal. This describes what each side has to do to get ticking warscore, i.e. additional warscore over time from having accomplished the goal. Wargoals include:

• Take province / Defend province: Control a specific province. This may be a province chosen on declaring the war, or the capital. Each side gets ticking warscore as long as they control the target. Neither side gets ticking warscore if a third party (e.g. rebels) controls it.
• Show superiority: Have at least 10% warscore from battles. No side gets ticking warscore if neither has said warscore from battles
• Blockade ports: Amount and rate of ticking warscore scales by the proportion of blockading.

Triggered

A triggered casus belli appears when certain actions are performed (like insulting other countries), and can also be given by events and missions. Triggered casus belli only last for a certain amount of time before they expire and are no longer valid. Without Art of War, none of these CBs can be used by an overlord on a subject's behalf.

• The duration of the CBs is listed in months.

Casus belli	Wargoal	Duration	modifier	modifier	cost modifier	Acquisition	Affected peace offers
Restoration of Union	Take capital	240	100%	100%	100%	Given by missions or to senior personal union partner when a junior partner becomes independent, for a total war score cost of 60%. Attacker is monarchy or Dutch Republic Defender is monarchy, Ambrosian Republic, or Naples after breaking to republican rebels Attacker is not a subject country	Form personal union
Defected Province	Take target province	12	100%	200%	50%	When a province defects due to rebels	Cede province Only on provinces that defected from the aggressor in the past 12 months
Canceled Loan	Superiority	12	100%	200%	75%	Given to debtor when creditor defaults on a loan This used to be such an easy way to get a CB that AI always refuses loans since 1.4 (except Indulgent rulers).	Gold Concede defeat Transfer trade power Steer trade
Discovered Spy	Superiority	12	100%	200%	75%	Given by two Japanese events involving ninja	Revoke core Gold Concede defeat
Disloyal Vassal	Take capital	120	100%	200%	50%	Given to overlord when a vassal breaks free	Demand vassalization
Imperial Liberation	Take target province	60	100%	200%	75%	Given to the Emperor when he demands unlawful territory and the other country refuses	Cede province Only on HRE provinces with the “Unlawful Territory” province modifier Cancel subject Release country Return core
Diplomatic Insult	Superiority	12	100%	200%	75%	By event and the "Send Insult" diplomatic action	Revoke core Gold Concede defeat Humiliation These options also affect the defender.
Subjugation	Take capital	120	100%	200%	50%	From vassalization missions and the Nobility estate when a diet is called	Demand vassalization
Obscure Documents	Take capital	12	100%	100%	150%	By Russian "Time of Troubles" disaster event "False Dimitri Overthrown"	Form personal union
Religious Unity	Take capital	24	100%	200%	75%	Given to the emperor when an HRE member refuses the emperor's demand for religious conformance	Force change religion
Border Friction	Take target province	12	75%	100%	75%	Some events	Cede province Only on neighbouring non-capital provinces Concede defeat
Trade War	Superiority	24	100%	200%	75%	By event Not to be confused with Trade Dispute or Trade Conflict.	Revoke core Gold Concede defeat Transfer trade power Steer trade Can't: Cede province Return core Revoke core Cancel subject Liberate country Demand vassalization Force tributary status Transfer vassals Form personal union
Trade Conflict	Blockade ports	24	100%	100%	100%	Via the "Justify Trade Conflict" covert action. Not available to Merchant Republics (they get their own version, see below).	Gold Concede defeat Transfer trade power Costs 50% less warscore Steer trade Can't: Cede province Return core Revoke core Cancel subject Liberate country Demand vassalization Force tributary status Transfer vassals Form personal union
Trade League Dispute	Blockade ports	24	100%	100%	100%	Available to the leader of a trade league against countries they could otherwise justify a trade conflict against.	Gold Concede defeat Transfer trade power Costs 50% less warscore Steer trade Can't: Cede province Return core Revoke core Cancel subject Liberate country Demand vassalization Force tributary status Transfer vassals Form personal union
Annexation War	Take capital	24	50%	100%	100%	Never This CB is broken and doesn't work properly, nor can it be obtained normally. It could have been a colonial conquest CB.
Government Form War	Take capital	120	75%	100%	100%	By event ( Milan's independent Catholic monarchy neighbours when it becomes an Ambrosian Republic, and Naples' independent Catholic monarchy neighbours when it becomes a republic with the Italian Signoria reform)	Force change government type Cede province Only on core, claimed, or neighbouring provinces
Forced ally to break alliance	Superiority	120	100%	200%	75%	Given when a Great Power forces an ally to break their alliance with the country.	Revoke core Gold Concede defeat Humiliation
Crush the Peasantry	Take capital	120	75%	100%	100%	Against HRE Peasant Republics (initially Dithmarschen and East Frisia) for the Emperor during the imperial incident “The Fate of the Peasantry” for neighbouring HRE non-republics after said incident if the empire voted to “Crush the remaining agitators.”	Force change government type Cede province Only on core, claimed, or neighbouring provinces
Peasant Revolt	Take capital	120	75%	100%	100%	For HRE Peasant Republics (initially Dithmarschen and East Frisia) against their non-republic HRE neighbours during the imperial incident “The Fate of the Peasantry” after said incident if the empire voted to “Grant concessions to the peasantry” and countries broke to peasant rebels at least 10 times during the incident.	Force change government type Cede province Only on core, claimed, or neighbouring provinces
Holy War Feast of Pheasants	Superiority	60	75%	125%	100%	With Emperor, given to Burgundy and (some) other European countries of the same religion against Ottomans when Burgundy completes the mission “Feast of Pheasants”. Attacker and defender belong to different religion groups Attacker and defender have different religions, taking syncretic religions into account	Cede province

Automatic

An automatic casus belli is given when certain conditions between the attacker and the defender are met. These last as long as the condition is still satisfied. The "advanced casus belli" are Imperialism and Nationalism and are gained at diplomatic technology 23.

Casus belli	Wargoal	Conditions	modifier	modifier	cost modifier	Affected peace offers
Humiliate Rival	Take capital	Attacker does not have a truce with defender Attacker is a player Defender is attacker's rival Attacker is not revolutionary	100%	125%	100%	Revoke core Gold Annul treaties Transfer trade power Steer trade Humiliate May Show Strength Costs 100% warscore and awards 30 power projection and 100 of each monarch power. Can't: Cede province Return core Cancel subject Release country Demand vassalization Transfer vassals Force tributary status Form personal union
Conquest	Take target province	Defender holds province with attacker's claim With Art of War, may be used by an overlord on a subject's behalf.	100%	100%	100%	Cede province Attacker: only on claimed provinces (0% cost) Defender: only on claimed or core provinces (0% cost)
Reconquest	Take target province	Defender holds province with attacker's core With Art of War, may be used by an overlord on a subject's behalf.	25%	100%	75%	Cede province Only on provinces attacker has a core on (0% cost) Return core (0% cost)
Independence	Defend capital	Attacker is a subject nation of defender, other than a colonial nation or tributary Either: Attacker does not have government reform Daimyo, and is not So with the Pirate Republic reform Defender does not have government form Shogunate	attacker: 100%	100%	75%	Concede defeat Independence granted for 23% war score
			defender: 50%			Cede province
Colonial Independence	Defend capital	Attacker is a colonial nation of defender	attacker: 100%	100%	75%	Concede defeat Independence granted for 23% war score
			defender: 50%			Cede province
Nationalism	Take target province	Attacker has diplomatic technology level 23 Attacker is not a subject nation, or is a tributary Defender holds a province in attacker's culture group Attacker is not revolutionary	50%	150%	50%	Cede province Only on provinces in victor's culture group
Imperialism	Take capital	Attacker has diplomatic technology level 23, or has Invasion modifier (only for Jan Mayen in an unmodded game) Attacker is not a subject nation, or is a tributary Attacker is not revolutionary Attacker does not have government reform “War Against the World Doctrine”	75%	100%	75%	Cede province (0% cost)
Contain Hegemon	Take capital	Attacker is not a hegemon Defender is a hegemon (requires Emperor)	75%	100%	75%	Cede province (0% cost)
War Against the World	Take capital	Attacker is not a subject nation, or is a tributary Attacker is not revolutionary Attacker has government reform “War Against the World Doctrine” (requires Pirate Republic government)	75%	100%	75%	Cede province (0% cost) Return core (50% cost)
War for the Emperor Subject Daimyo attacking the Shogun	Take capital	Attacker is a vassal or junior personal union partner of defender Attacker has government reform Daimyo, or is So with the Pirate Republic government reform Defender has government reform Shogunate Attacker is not revolutionary	75%	100%	100%	Cede province Only on claimed provinces
War for the Emperor Independent Daimyo attacking the Shogun	Take capital	Attacker is not a subject country Attacker has government reform Daimyo, or is So with the Pirate Republic government reform Defender has government reform Shogunate Attacker is not revolutionary	75%	100%	100%	Cede province Only on claimed provinces
Annex Daimyo	Take capital	Attacker has government reform Shogunate Defender has government reform Daimyo and is a subject of the shogun, or is So with the Pirate Republic government reform Defender owns at least 10 provinces, or is independent Attacker is not revolutionary	50%	100%	100%	Cede province Only on claimed provinces
Sengoku	Take capital	Attacker and defender both: Are subject countries Have government form Daimyo and are subjects of the shogun, or are So with the Pirate Republic government reform Attacker neighbours defender Attacker is not revolutionary	75%	100%	100%	Cede province Only on claimed provinces
Colonialism	Take target colony	Attacker has a colonial claim against defender. This means: Attacker or their subject colonial nation owns land that is overseas for attacker Defender owns land that is overseas for them or they are a colonial subject These respective provinces neighbour each other Attacker is not revolutionary	25%	100%	50%	Cede province Only on the provinces that could trigger the CB for either side
Liberation	Take capital	Available to France after completing the mission "American Independence", otherwise only used in historical wars	100%	300%	75%	Cancel subjects Release country Return core
Holy War	Superiority	Attacker does not have the tier 8 theocracy government reform “The Global Crusade” Attacker neighbours defender Attacker and defender belong to different religion groups Attacker and defender have different religions, taking syncretic religions into account One of: Attacker has Religious idea "Deus Vult" Attacker is Catholic, and the Curia controller has declared a crusade on defender With Emperor: attacker is Muslim, and their religion's tier 3 or higher Defender of the Faith has declared a jihad on the target province (Jerusalem, Mecca, or Medina) because it is owned by a non-Muslim country Attacker is not revolutionary	75%	125%	100%	Cede province
Defender of the Faith	Defend country	Attacker is Defender of the Faith Attacker neighbours defender Attacker and defender have different religions, taking syncretic religions into account Attacker has Religious idea "Deus Vult" Attacker is not revolutionary One of: Peace of Westphalia has not occurred (Always true if Art of War is not active.) Attacker and defender are not both members of the Holy Roman Empire	100%	200%	75%	Cancel subject Release country Return core Revoke core Gold Concede defeat
Cleansing of Heresy	Superiority	Attacker neighbours defender Attacker has Religious idea "Deus Vult", or defender had event “The Heretic King” since the last change of ruler and chose the option “Stay true to Christ!” Attacker and defender belong to the same religion group Attacker and defender have different religion, taking syncretic religions into account If Art of War is active and attacker and defender are both in the HRE: the Peace of Westphalia has not occurred Attacker is not revolutionary	75%	200%	100%	Force change religion Cede province
Excommunication War / Excommunicated Ruler	Superiority	Attacker is Catholic and not excommunicated Defender is Catholic and is excommunicated Attacker neighbours defender One of: Peace of Westphalia has not occurred (Always true if Art of War is not active.) Attacker and defender are not both members of the Holy Roman Empire Attacker is not revolutionary	50%	125%	100%	Cancel subject Release country Return core Cede province Only on core, claimed or neighbouring provinces owned by excommunicated Catholics Revoke core Demand vassalization Gold Concede defeat
Trade Dispute	Superiority	One of: Defender embargoes attacker, but attacker does not embargo defender Both countries are Merchant Republics Attacker is not revolutionary	100%	200%	75%	Revoke core Gold Concede defeat Transfer trade power Steer trade Can't: Cede province Return core Revoke core Cancel subject Transfer vassals Liberate country Demand vassalization Force tributary status Form personal union
Trade League Dispute	Superiority	Attacker is leader of a trade league Attacker is not embargoed by defender A member of attacker's trade league is embargoed by defender Attacker is not revolutionary	100%	200%	75%	Revoke core Gold Concede defeat Transfer trade power Steer trade Can't: Cede province Return core Revoke core Cancel subject Liberate country Demand vassalization Transfer vassals Force tributary status Form personal union
Imperial Ban	Take target province	Attacker is Holy Roman Emperor Imperial reform “Call for Reichsreform” has been enacted Defender is not in HRE, but holds an HRE province Attacker is not revolutionary	100%	200%	75%	Cancel subject Release country Return core Cede province Only on HRE provinces held by non-HRE country. Cannot demand non-HRE provinces even for normal cost
Coalition	Superiority	Attacker is in a coalition against defender Defender is not already in a coalition war Coalition has at least 3 members Attacker's opinion towards defender is affected by aggressive expansion Attacker is not revolutionary	10%	100%	75%	Cancel subject Release country Return core Revoke core Gold Concede defeat Cede province Only on core provinces The attacking war leader gets +30 war enthusiasm with this CB.
Claim on Throne	Take capital	Attacker has a succession claim on defender Attacker is not revolutionary	attacker: 100%	200%	140%	Form personal union (84% war score cost)
			defender: 50%	100%	75%	Cede province Only on core provinces
Tribal Conquest	Superiority	Attacker neighbours defender Attacker is Steppe Nomad Defender is not Steppe Nomad Attacker is not revolutionary	75%	100%	100%	Cede province Demand vassalization Force tributary status Gold
Tribal Feud	Take target province	Both countries are Steppe Nomads Attacker neighbours defender Attacker is not revolutionary	75%	100%	100%	Cede province Demand vassalization Force tributary status Gold
Revoke Electorate	Take capital	Common Sense is not active Use "Revoke Electorate" diplomatic action instead. Art of War is not active Apparently it breaks the religious league system. Attacker is Holy Roman Emperor Defender is an elector Attacker and defender have different religion Attacker is not revolutionary	100%	200%	75%	Revoke electorate
Liberate Elector	Superiority	Attacker is Holy Roman Emperor Defender has an elector subject Attacker is not revolutionary	100%	150%	75%	Cancel subject Release country Return core
Trade Protection	Blockade ports	Attacker's home trade node, or one where they have a merchant: Attacker has at least 10% share of trade power Defender's privateers have at least 1% share of trade power Attacker is not revolutionary	100%	100%	100%	Gold Concede defeat Transfer trade power Costs half amount of warscore Steer trade
Crush the Revolution	Take capital	Attacker's capital is in Europe, or attacker neighbours defender Attacker is not revolutionary Attacker does not have a truce or alliance with defender Attacker is not a subject, or is a tributary Attacker does not have a truce with defender Defender is revolutionary	50%	150%	50%	Demand vassalization Cede province Revoke core Cancel subject Release country Gold Concede defeat Annul treaties (Attacker only) Dismantle the revolution (Defender only) Spread the revolution Both sides get an additional +50 war enthusiasm when at war with this CB.
Spread the Revolution	Superiority	Attacker is revolutionary Attacker is a player, or attacker's capital is in Europe, or attacker is the revolution target Defender is not attacker's subject Defender is not revolutionary	50%	150%	50%	Demand vassalization Cede province Revoke core Cancel subject Release country Gold Annul treaties (Attacker only) Spread the revolution (Defender only) Dismantle the revolution
Unify China	Superiority	Attacker is not a subject nation, or is a tributary If the Mandate of Heaven expansion is active: Attacker is the emperor of China Defender's primary culture is in Chinese group Otherwise: Attacker's primary culture in Chinese group If attacker's primary culture is Manchu, attacker is Manchu or Qing Defender owns at least one province in North China, Xinan, or South China region Defender does not have the “Mandate of Heaven” modifier Attacker neighbours defender	50%	150%	50%	Attacker: Cede province Only on provinces in the China superregion
						Defender: Cede province Only on provinces in the South China, Xinan or South China region or with culture in the same group as defender
Take Mandate of Heaven	Take capital	The Mandate of Heaven expansion is active Attacker is not a subject country Attacker neighbours defender Attacker does not have government reform Shogunate Defender is the Emperor of China Attacker's religion is in pagan or Eastern group Attacker does not have a truce with defender Attacker is not revolutionary	50%	100%	50%	Attacker: Cede province Take Mandate of Heaven
						Defender: Cede province
Humiliate	Take capital	The Conquest of Paradise expansion is active Attacker's government is Native Attacker does not have a truce with defender Both attacker and defender only own one province Attacker neighbours defender Attacker is not revolutionary	0%	0%	0%	Humiliate Can't annex enemies
Religious League	Superiority	The Art of War expansion is active Neither country is already in a league war Defender is Holy Roman Emperor Attacker is league leader Attacker is heretic to HRE Attacker is in opposing league Attacker is not revolutionary	50%	150%	50%	Demand vassalization Cede province Revoke core Cancel subject Release country Force change religion Gold Annul treaties Religious supremacy Both sides get an additional +50 war enthusiasm when at war with this CB.
Support Rebels	Take capital	The Art of War expansion is active Rebel faction that attacker is supporting has risen in revolt against defender	100%	200%	50%	(Attacker only) Enforce rebel demands While at war with this CB, the targeted rebels' armies are friendly to attacker.
Maya Confederation	Take target province	The El Dorado expansion is active Attacker has Mayan religion Attacker is not a subject nation, or is a tributary Attacker has not enacted all religious reforms Defender is not a subject of attacker Defender is in pagan religious group Attacker neighbours defender	75%	100%	75%	Cede province
Flower Wars	Take capital	The El Dorado expansion is active Attacker's religion is Nahuatl Attacker is not a subject nation, or is a tributary Attacker has not reformed the religion Defender is not a subject of attacker Attacker neighbors defender	100%	200%	50%	Demand vassalization
Force Migration	Take capital	The Cossacks expansion is active Attacker neighbors defender Attacker is not a subject nation, or is a tributary Defender is not a subject nation, or is a tributary Defender is a migratory nation	100%	100%	100%	(Attacker only) Force migration Can't: Cede province (but can cede provinces from secondary participants in primary peace deal) Return core (this doesn't affect separate peace deals) Demand vassalization (this doesn't affect separate peace deals) Transfer vassals (this doesn't affect separate peace deals) Force tributary status (this doesn't affect separate peace deals)
Force Tributary State	Take capital	Mandate of Heaven expansion is active Attacker is Emperor of China Defender is not a subject nation Attacker neighbors defender	50%	200%	50%	Force tributary status (0% cost)
Expand Empire	Take capital	The Emperor expansion is active Attacker is the Holy Roman Emperor The reform “Absolute Reichsstabilität” has been passed Defender is a valid target for the "Expand empire" peace deal Defender is in the same religion group as attacker Defender is on the same continent as attacker Defender is not a member of the Holy Roman Empire Defender neighbours any province that is part of the empire	100%	25%	100%	(Attacker only) Expand empire (Defender only) Cede province
Great Holy War	Superiority	Attacker has the tier 8 theocracy government reform "The Global Crusade" One of: Attacker neighbours defender Attacker has a claim on defender Attacker has Religious idea "Deus Vult" Defender is in pagan religious group, and attacker has completed Expansion or Exploration ideas or has the "Mission to Civilize" tier 2 government reform Attacker and defender belong to different religion groups Attacker and defender have different religions, taking syncretic religions into account Attacker is not revolutionary	75%	200%	75%	Cede province Cancel subject (Attacker only) Force change religion

Conquest details

Having a claim allows the selection of the targeted province as a wargoal. The covert Fabricate Claims diplomatic action provides a claim on a single province (for details of which provinces can have claims fabricated on them, see Espionage § Covert actions). This is an immediate action that costs a certain number of points of spy network strength, starting at 20 and increasing by 5 spy network points per existing claim. In addition, many missions, events and unification national decisions give permanent or temporary claims, sometimes on a large region. There are also some events, such as Border Friction, that allow claims to be gained.

A temporary claim will expire in 25 years after a nation first gets the claim (permanent claims never expire). A claim can't expire during a war with the province's owner; permanent claims never expire, though they can still be given up in a peace deal. Regardless of CB used, claims provide −10% core creation cost, or −25% for a permanent claim.

Choosing a CB

Conquest is ordinarily the easiest CB to get by simply fabricating a claim, but also the least useful. Taking too many provinces can quickly result in a large coalition being formed against the country due to aggressive expansion (AE). It is still desirable to fabricate claims before fighting, in order to reduce coring cost and time, and the diplomatic point cost.

• Holy War and Cleansing of Heresy work on any heathen or heretic, which also removes diplomatic point cost for taking any province, and are both unlocked by the last Religious idea.
• If you have a special CB due to your government form or religion that allows you to take land, you'll usually be better off using it when possible, since it's tailored to your needs. Claims are still useful in these situations, but not strictly necessary. Daimyo, Maya reforming the religion, the Emperor of China, and steppe hordes all want to conquer land with less AE and maybe warscore cost, while Nahuatl trying to reform the religion want cheaper vassalization. The revolution target wants to Spread the Revolution (in fact it can hardly do much more), while their monarchist neighbours want to Crush the Revolution.
  • Becoming revolutionary is a common world conquest strategy, because the bonuses of being the revolution target and the reduced warscore and diplomatic power cost of the revolutionary CB, in combination with administrative efficiency from high absolutism, make it possible to conquer huge amounts of land very quickly.
• Note that a casus belli only reduces the cost of provinces that fulfill its criteria. For instance, Colonialism has 25% aggressive expansion and 50% warscore cost, but only for taking provinces that are overseas for both or from overseas colonial nations. Provinces on the same continent as the target's capital or directly connected to the capital will incur full costs (unless they're a colonial nation). When choosing such a CB, it will list the names of all the applying provinces, or show the number of these provinces if there are too many.
• Also note that the reduced warscore cost also affects options that are set on total province cost. So if a country's warscore cost is just over 100, the reduced cost for being wargoal might just make the country annexable/vassalizable.

If the goal of the war is not to seize territory or force-vassalize, then the choice of CB is less important, since extorting money or releasing nations doesn't cause AE. Conquest is fine to use in such a situation. If the country happens to be a rival and releasing vassals or countries is not desired, the special Humiliate Rival CB is ideally suited for this purpose. The drawback is that allies can't be called in on a promise of land with a CB that can't be used to fulfil that promise, so you will need favours.

Mechanics

Defense

Fort • Zone of control

External relations=

Customization

Nation designer • Random New World

Ages and Institutions

Ages • Institutions

Innovativeness and Technology

Innovativeness • Technology